Medium conveyance device and image forming device

ABSTRACT

A medium conveyance device includes a medium setting part on which a medium is set, a first roller coming in contact with the medium set on the medium setting part and sending out the medium in a conveyance direction, a second roller situated on a downstream side of the first roller in the conveyance direction and conveying the medium sent out by the first roller, and a medium contact part arranged in a conveyance path between the first roller and the second roller and coming in contact with the medium. The medium contact part has a plurality of contact surfaces switchable according to a type of the medium and differing in shape.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a medium conveyance device for conveying a medium and an image forming device including the medium conveyance device.

2. Description of the Related Art

A medium conveyance device used for an image forming device sends out a sheet (medium) loaded on a tray with a pickup roller, separates the sheet from other sheets one by one with a feed roller and a separation roller, and sends out the sheet to a conveyance path. Such a medium conveyance device is described in Japanese Patent Application Publication No. 2013-129481 (FIG. 4), for example.

Here, in order to prevent the multifeed in which a plurality of sheets overlapping on each other are conveyed at the same time, it is conceivable that a rib (contact part) for coming in contact with a front end of the sheet is provided in the conveyance path of the sheet between the pickup roller and the feed roller.

However, there have been a type of sheet which is likely to fail to climb over the rib and cause a conveyance error, and another type of sheet which is likely to climb over the rib and cause the multifeed.

SUMMARY OF THE INVENTION

The object of the present invention, which has been made to resolve the above-described problem, is to inhibit the conveyance error and the multifeed which are caused according to a type of medium.

A medium conveyance device according to an aspect of the present invention includes a medium setting part on which a medium is set, a first roller coming in contact with the medium set on the medium setting part, the first roller sending out the medium in a conveyance direction, a second roller situated on a downstream side of the first roller in the conveyance direction, the second roller conveying the medium sent out by the first roller, and a medium contact part arranged in a conveyance path between the first roller and the second roller, the medium contact part coming in contact with the medium. The medium contact part has a plurality of contact surfaces switchable according to a type of the medium, the plurality of contact surfaces differing in shape.

An image forming device according to another aspect of the present invention includes the above-described medium conveyance device, and an image forming section that forms an image on the medium conveyed by the medium conveyance device.

According to the present invention, the medium contact part has a plurality of contact surfaces differing in shape and the switching between the contact surfaces is made according to the type of the medium, and thus the conveyance error and the multifeed can be inhibited for both of the medium having high stiffness and the medium having low stiffness.

BRIEF DESCRIPTION OF THE DRAWINGS

In the attached drawings,

FIG. 1 is a diagram showing the basic configuration of an image forming device in a first embodiment;

FIG. 2 is a schematic diagram showing a process unit of the image forming device in the first embodiment;

FIGS. 3A and 3B are a perspective view showing a part of the image forming device including a manual feed tray in the first embodiment and a perspective view showing a state in which a manual feed tray cover has been opened;

FIG. 4 is a perspective view showing a state in which the manual feed tray cover of the image forming device in the first embodiment has been opened and a lever has been raised;

FIG. 5 is a perspective view showing a medium conveyance device in the first embodiment;

FIG. 6 is a sectional side view showing the medium conveyance device in the first embodiment;

FIG. 7 is a perspective view showing a retard roller and a retard frame in the first embodiment;

FIGS. 8A and 8B are a perspective view showing the retard frame in the first embodiment and its vicinity, and a perspective view showing the retard frame without a cover;

FIGS. 9A and 9B are a perspective view and an enlarged view showing the retard frame, regulatory ribs, separatory dams and their vicinity in the first embodiment;

FIGS. 10A and 10B are a perspective view and an enlarged view showing a state in which the separatory dams in the first embodiment are at lowered positions;

FIG. 11 is a cross-sectional view showing the medium conveyance device in the first embodiment;

FIG. 12 is a block diagram showing a control system of the image forming device in the first embodiment;

FIGS. 13A and 13B are schematic diagrams showing conveyance states of thick paper and thin paper by the medium conveyance device in the first embodiment;

FIGS. 14A and 14B are a cross-sectional view and an enlarged view showing a state in which the medium conveyance device in the first embodiment is conveying thick paper;

FIGS. 15A and 15B are a cross-sectional view and an enlarged view showing a state in which the medium conveyance device in the first embodiment is conveying thin paper;

FIG. 16 is a sectional side view showing a medium conveyance device in a second embodiment; and

FIG. 17A is a cross-sectional view showing the medium conveyance device in the second embodiment, and FIGS. 17B and 17C are diagrams magnifying a part of the medium conveyance device.

DETAILED DESCRIPTION OF THE INVENTION

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications will become apparent to those skilled in the art from the detailed description.

First Embodiment Configuration of Image Forming Device

First, an image forming device 1 in a first embodiment including a manual feed tray 30 will be described. FIG. 1 is a diagram showing the image forming device 1 in the first embodiment. The image forming device 1 is a printer that forms a color image by means of electrophotography.

The image forming device 1 includes a sheet tray 50 storing sheets S, a send-out section 51 that sends out the sheet S on the sheet tray 50, a manual feed tray 30 that feeds a sheet P (FIG. 14A) as a medium, a medium conveyance section 55 that conveys the sheet S (P) fed from the sheet tray 50 or the manual feed tray 30, an image forming section 60 that forms a toner image on the sheet S (P), a fixation device 80 that fixes the toner image on the sheet S (P), and an ejection section 85 that ejects the sheet S (P) on which the toner image has been fixed.

The sheet tray 50 is arranged in a lower part of the image forming device 1 and stores the sheets S (media) in the stacked state. The send-out section 51 includes a pickup roller 52 that sends out the sheet S stored in the sheet tray 50 and a feed roller 53 and a separation piece 54 that separate the sheet S sent out by the pickup roller 52 from other sheets S and send out the sheet S one by one.

The manual feed tray 30 is arranged in a lateral part of the image forming device 1. The manual feed tray 30 includes a sheet setting plate 32 on which the sheets P in the stacked state are set, a manual feed tray cover 31 that rotatably holds the sheet setting plate 32, a pickup roller (first roller) 34 that sends out the sheet P on the sheet setting plate 32, and a feed roller (second roller) 35 and a retard roller (separation roller) 36 that separate the sheet P sent out by the pickup roller 34 from other sheets one by one.

The medium conveyance section 55 includes two conveyance roller pairs 56 and 57. The conveyance roller pair 56 conveys the sheet P sent out by the send-out section 51. The conveyance roller pair 57 conveys the sheet P conveyed from the conveyance roller pair 56 or the sheet S fed from the manual feed tray 30 to the image forming section 60.

The image forming section 60 includes four process units 61K, 61Y, 61M and 61C for forming toner images of black (K), yellow (Y), magenta (M) and cyan (C) and a transfer section 70 that transfers the toner images to a surface of the sheet.

The process units 61K, 61Y, 61M and 61C are arranged from an upstream side to a downstream side in a conveyance direction of the sheet S (P) (from right to left in the drawing). Each of the process units 61K, 61Y, 61M and 61C will be referred to as a process unit 61 when it is not particularly necessary to distinguish between the units 61K, 61Y, 61M and 61C.

FIG. 2 is a schematic diagram showing an example of the configuration of the process unit 61. The process unit 61 includes a photosensitive drum 62 as an image carrier, a charging roller 63 as a charging member for uniformly charging the surface of the photosensitive drum 62, a print head 64 as an exposure device for applying light to the photosensitive drum 62 and thereby forming an electrostatic latent image, a development roller 65 as a developing agent carrier for developing the electrostatic latent image on the photosensitive drum 62, a supply roller 66 as a supply member for supplying a toner (developing agent) to the development roller 65, and a toner cartridge 67 as a developing agent container for supplying the toner to the development roller 65 and the supply roller 66.

Returning to FIG. 1, the transfer section 70 includes a transfer belt 71 that conveys the sheet S (P), four transfer rollers 72 respectively facing the photosensitive drums 62 of the process units 61 via the transfer belt 71, a drive roller 73 that drives the transfer belt 71, and a tension roller 74 that gives tension to the transfer belt 71. The transfer section 70 transfers the toner image of each color formed on the photosensitive drum 62 of each process unit 61 to the sheet S (P) by means of Coulomb force.

The fixation device 80 includes, for example, a fixation roller 81 having a built-in heat source and a pressure roller 82 pressed against the fixation roller 81. The fixation roller 81 and the pressure roller 82 apply heat and pressure to the toner images transferred to the sheet S (P) and thereby fix the toner images on the sheet S (P).

The ejection section 85 includes a conveyance roller pair 83 for conveying the sheet S (P) which has passed through the fixation device 80 and an ejection roller pair 84, and ejects the sheet S (P) on which the fixation has been completed. An upper cover of the image forming device 1 is provided with a stacker part 86 on which the sheets S (P) ejected by the ejection section 85 are loaded.

Incidentally, while the image forming device 1 includes a double-side printing unit 87 that conveys the sheet S (P) which has passed through the fixation device 80 towards the medium conveyance section 55 for the double-side printing, the description of the double-side printing unit 87 is left out.

In FIG. 1, the moving direction of the sheet S (P) when the sheet passes through the image forming section 60 is defined as an X direction, and the direction of a rotation axis of the photosensitive drum 62 is defined as a Y direction. The Y direction is the same as a width direction of the sheet S (P). A direction orthogonal to both of the X direction and the Y direction is defined as a Z direction. In this description, the Z direction is assumed to be the vertical direction.

Configuration of Medium Conveyance Device

FIGS. 3A and 3B are perspective views showing a part of the image forming device 1 including the manual feed tray 30 viewed from obliquely above. FIG. 3A shows a state in which the manual feed tray 30 is at a storage position, that is, a state in which the manual feed tray cover 31 has been closed. FIG. 3B shows a state in which the manual feed tray 30 is at a usage position, that is, a state in which the manual feed tray cover 31 has been opened. FIG. 4 shows a state in which the manual feed tray 30 is at the usage position and a lever 33 has been raised.

As shown in FIG. 3B, the manual feed tray cover 31 is rotatably attached to a device frame 10 as a frame member fixed to a main body of the image forming device 1. The manual feed tray cover 31 rotates between a closed position shown in FIG. 3A and an open position shown in FIG. 3B. The sheet setting plate 32 is provided on the manual feed tray cover 31 to be rotatable as will be described later, and the sheets P are set on the sheet setting plate 32.

Further, a lock part 31 b for locking the manual feed tray cover 31 at the closed position to the main body of the image forming device 1 is formed on each side of the manual feed tray cover 31 in the Y direction. In the closed position shown in FIG. 3A, when the user releases the lock by operating the lock parts 31 b and pulls the manual feed tray cover 31 forward, the manual feed tray cover 31 rotates around a rotary support part 10 a (FIG. 8A) of the device frame 10 towards the open position.

The manual feed tray 30 and the device frame 10 constitute a medium conveyance device. Further, the manual feed tray cover 31 and the sheet setting plate 32 constitute a medium setting part. A part of the image forming device 1 other than the medium conveyance device (the manual feed tray 30 and the device frame 10) will be referred to as the main body (based body) of the image forming device 1.

A holding member 11 rotatably holding the pickup roller 34 is held by the device frame 10 to be rotatable. The holding member 11 extends in the Y direction and has a pair of arms 11 a on both sides in the Y direction (only one arm 11 a is shown in FIG. 3B). A tip end part of each arm 11 a slidably engages with a guide groove 31 a (FIG. 5) formed on the manual feed tray cover 31 and a rotation range of the manual feed tray cover 31 is limited.

As shown in FIG. 4, the lever 33 is rotatably held by the holding member 11. The lever 33 extends in the Y direction and has a pair of arms 33 a on both sides (only one arm 33 a is shown in FIG. 4). A tip end of each arm 33 a engages with a groove 32 a formed at a Y direction end of the sheet setting plate 32. As shown in FIG. 3B, when the user rotates the lever 33, the sheet setting plate 32 moves up and down by the engagement of the arms 33 a and the grooves 32 a.

FIG. 5 is a perspective view showing the manual feed tray 30 at the open position and the device frame 10. FIG. 6 is a cross-sectional view of the manual feed tray 30 and the device frame 10 viewed in the direction indicated by the arrow VI in FIG. 5 (i.e., viewed from the +Y side). Incidentally, a part of the holding member 11 and the lever 33 are omitted in FIG. 5.

In FIG. 5, the pickup roller 34 as the first roller is rotatably held by the holding member 11. The pickup roller 34 is provided so as to come in contact with a contact part 32 b (FIG. 6) formed in a central part of the sheet setting plate 32 in regard to the Y direction.

As shown in FIG. 6, an end part of the sheet setting plate 32 in the −X direction (i.e., end part on the upstream side in the conveyance direction indicated by the arrow A) is rotatably held by the manual feed tray cover 31. Further, under the contact part 32 b of the sheet setting plate 32, a spring 45 as a coil spring is arranged in a compressed state. By this spring 45, the contact part 32 b of the sheet setting plate 32 is pressed towards the pickup roller 34.

The feed roller 35 as the second roller is supported by the device frame 10 to be rotatable. When the manual feed tray 30 is at the open position, the feed roller 35 is situated on the downstream side of the pickup roller 34 in the conveyance direction (indicated by the arrow A). The feed roller 35 is rotated clockwise in the drawing by a sheet feed motor 224 (FIG. 12) via an electromagnetic clutch 225 (FIG. 12).

The holding member 11 rotatably holding the pickup roller 34 is held by the device frame 10 to be rotatable around a rotation axis coaxial with the feed roller 35. The pickup roller 34 and the feed roller 35 are connected to each other by an idle roller 38 (FIG. 5) held by the holding member 11 to be rotatable.

Thus, the pickup roller 34 rotates in the same direction as the feed roller 35, following the rotation of the feed roller 35. Further, the pickup roller 34 rotates around the feed roller 35 in association with the rotation of the holding member 11 while maintaining the state of being connected with the feed roller 35.

The retard roller 36 as the separation roller is arranged under the feed roller 35 to face the feed roller 35. FIG. 7 is a perspective view showing the retard roller 36 and a retard frame 40 holding the retard roller 36.

As shown in FIG. 7, the retard frame 40 includes a pair of side plates 41 facing each other in the Y direction, and a groove part 41 a is formed on each side plate 41. The retard roller 36 is attached to a rotary shaft 42 via a torque limiter 37, and each end part of the rotary shaft 42 is fitted in the groove part 41 a. When the retard roller 36 receives turning force from outside, the retard roller 36 rotates in the direction of the turning force while generating a predetermined rotational load by the torque limiter 37.

On each side plate 41 of the retard frame 40, a groove part 41 b is formed to engage with a shaft part 15 (FIG. 8a ) formed on the device frame 10. The retard frame 40 is rotatably supported by the device frame 10 under the feed roller 35 by the engagement of the shaft part 15 and the groove part 41 b. Both of the rotation axis of the retard frame 40 and the rotation axis of the retard roller 36 are parallel to the rotation axis of the feed roller 35 (i.e., in the Y direction).

Returning to FIG. 6, the device frame 10 is provided with a conveyance guide 13 that guides the sheet S sent out from the send-out section 51 (FIG. 1) or the sheet P fed from the manual feed tray 30 to the conveyance roller pair 57.

Further, conveyance rollers 57 a and 57 b in the image forming device 1 constitute the conveyance roller pair 57 (FIG. 1) for conveying the sheet S sent out from the send-out section 51 (FIG. 1) and the sheet P fed from the manual feed tray 30. The conveyance rollers 57 a and 57 b are attached to the main body of the image forming device 1 to be rotatable and are rotated by a conveyance motor 226 (FIG. 12).

FIG. 8A is a perspective view showing the retard frame 40, a regulatory rib 21 and their vicinity. FIG. 8A shows the device frame 10 while cutting it at a position on the front side (+Y side) of the retard frame 40. The same applies to FIG. 9A and FIG. 10A which will be explained later.

As shown in FIG. 8A, an inclined surface 14 facing a side of the manual feed tray 30 (FIG. 6) is formed on the device frame 10. The retard frame 40 is arranged at the Y direction center of the inclined surface 14. As mentioned earlier, the shaft part 15 of the device frame 10 engages with the groove parts 41 b of the retard frame 40, and thereby the retard frame 40 is supported to be rotatable around a rotation axis in the Y direction.

Further, in the device frame 10, a spring seat 43 is formed under the retard frame 40. Between the spring seat 43 and the retard frame 40, a spring 44 as a coil spring is arranged in a compressed state. The spring 44 presses the retard frame 40 in a direction to press the retard roller 36 against the feed roller 35.

A cover 46 that covers the upstream side of the retard roller 36 in the conveyance direction (indicated by the arrow A) is attached to an upper part of the retard frame 40. The cover 46 is attached to the side plates 41 of the retard frame 40 so as to expose the top (i.e., the side of the feed roller 35) of the retard roller 36.

FIG. 8B is a perspective view in which the cover 46 has been removed from the retard frame 40 shown in FIG. 8A. As shown in FIG. 8B, in the device frame 10, a pair of regulatory ribs 21 are formed to adjoin both outer sides of the pair of side plates 41 of the retard frame 40 in regard to the Y direction. Incidentally, only one regulatory rib 21 is shown in FIGS. 8A and 8B. The regulatory rib 21 is formed like a flat plate having a plate surface parallel to the XZ plane.

The regulatory rib 21 has a contact surface 21 a facing the conveyance path of the sheet P and having a curvature radius R1. The contact surface 21 a is formed at an end part of the regulatory rib 21 situated on the upstream side in the conveyance direction (indicated by the arrow A) and at the upper end (end in the +Z direction).

The contact surface 21 a of the regulatory rib 21 is situated between the pickup roller 34 and the feed roller 35 in the conveyance direction indicated by the arrow A as shown in FIG. 11 which will be explained later. The contact surface 21 a of the regulatory rib 21 has functions of guiding the sheet P and inhibiting the multifeed of the sheets P.

FIG. 9A is a perspective view showing the retard frame 40, the regulatory ribs 21, separatory dams 22 and their vicinity. As shown in FIG. 9A, the separatory dams 22 are provided further on both outer sides of the pair of regulatory ribs 21 in regard to the Y direction. The separatory dam 22 is a plate-like member having a plate surface parallel to the XZ plane and has a projecting piece 22 c projecting in the conveyance direction indicated by the arrow A.

The separatory dam 22 has a contact surface 22 a facing the conveyance path of the sheet P and having a curvature radius R2 (<R1). The contact surface 22 a is formed at an end part of the separatory dam 22 in the −X direction (i.e., end on the upstream side in the conveyance direction) and in the +Z direction (namely, upper end). The contact surface 22 a of the separatory dam 22 has functions of guiding the sheet P and inhibiting the multifeed of the sheets P.

The regulatory rib 21 and the separatory dam 22 constitute a medium contact part that comes in contact with the sheet P in the conveyance path between the pickup roller 34 and the feed roller 35 and them. The regulatory rib 21 constitutes a fixed part of the medium contact part, while the separatory dam 22 constitutes a movable part of the medium contact part.

FIG. 9B is an enlarged view showing the retard frame 40, the regulatory ribs 21 and the separatory dams 22. As shown in FIG. 9B, the separatory dam 22 is a plate-like member having a plate surface parallel to the XZ plane. A guide hole 22 b in a quadrangular shape, for example, is formed substantially at the center of the separatory dam 22. A guide rib 21 b in a quadrangular shape formed on the regulatory rib 21 engages with the guide hole 22 b.

The X direction dimension of the guide hole 22 b is substantially equal to or slightly greater than the X direction dimension of the guide rib 21 b. In contrast, the Z direction dimension of the guide hole 22 b is greater than the Z direction dimension of the guide rib 21 b.

Namely, by the engagement of the guide rib 21 b and the guide hole 22 b, the separatory dam 22 is supported by the regulatory rib 21 to be movable in the z direction. In the state shown in FIGS. 9A and 9B, the separatory dam 22 is at an upper end position (end position in the +Z direction) in the movable range.

When the separatory dam 22 is at the upper end position, the contact surface 22 a of the separatory dam 22 is situated above the contact surface 21 a of the regulatory rib 21. Accordingly, the contact surface 22 a of the separatory dam 22 projects into the conveyance path of the sheet P.

FIG. 10A is a perspective view showing the retard frame 40, the regulatory ribs 21, the separatory dams 22 and their vicinity when the separatory dams 22 are at lower end positions. FIG. 10B is an enlarged perspective view showing the retard frame 40, the regulatory ribs 21 and the separatory dams 22 when the separatory dams 22 are at the lower end positions.

As shown in FIG. 10B, when the separatory dam 22 is at the lower end position in the movable range, the contact surface 22 a of the separatory dam 22 withdraws downward compared to the contact surface 21 a of the regulatory rib 21. Accordingly, the contact surface 21 a of the regulatory rib 21 projects into the conveyance path of the sheet P.

FIG. 11 is a cross-sectional view showing the device frame 10 and the manual feed tray 30. As shown in FIG. 11, the projecting pieces 22 c of the pair of separatory dams 22 are connected to each other by a connection bar 23 extending in the Y direction.

The device frame 10 is provided with a rotatable switching lever 25. The switching lever 25 includes a rotary shaft 25 a arranged under the connection bar 23, an operation part 25 b extending in the −X direction from the rotary shaft 25 a, and an action part 25 c projecting from the rotary shaft 25 a towards the connection bar 23. The operation part 25 b and the action part 25 c are combined together in an L-shape. The rotary shaft 25 a is parallel to the Y direction.

The operation part 25 b, projecting in the -X direction from the device frame 10, is operated by the user. The action part 25 c comes in contact with the connection bar 23 from below.

In the state shown in FIG. 11, the separatory dam 22 is at the lower end position in the movable range in the z direction.

In contrast, when the user pushes the operation part 25 b of the switching lever 25 downward, the switching lever 25 rotates clockwise around the rotary shaft 25 a. Accordingly, the action part 25 c of the switching lever 25 comes in contact with the connection bar 23 from below and presses the connection bar 23 upward. Consequently, the separatory dam 22 moves to the upper end position in the movable range in the z direction.

As mentioned earlier, when the separatory dam 22 is at the upper end position in the movable range, the contact surface 22 a of the separatory dam 22 is situated above the contact surface 21 a of the regulatory rib 21, and the contact surface 22 a of the separatory dam 22 projects into the conveyance path of the sheet P. When the separatory dam 22 is at the lower end position in the movable range, the contact surface 22 a of the separatory dam 22 withdraws downward compared to the contact surface 21 a of the regulatory rib 21, and the contact surface 21 a of the regulatory rib 21 projects into the conveyance path of the sheet P.

Control System of Image Forming Device

Next, a control system of the image forming device 1 will be described. FIG. 12 is a block diagram showing the control system of the image forming device 1. The image forming device 1 includes a control section 200, an I/F (interface) control section 201, a reception memory 202, an image data editing memory 203, an operation section 204, a sensor group 205, a power supply control section 206, a head control section 211, a drive control section 212, a belt drive control section 214, a fixation control section 216, a fixation drive control section 219 and a sheet supply conveyance control section 221.

The control section 200 includes a microprocessor, a ROM (Read Only Memory), a RAM (Random Access Memory), an input/output port, a timer, and so forth. The control section 200 receives print data and a control command from a host device via the I/F control section 201 and performs a print operation of the image forming device 1.

The reception memory 202 temporarily stores the print data inputted from the host device via the I/F control section 201. The image data editing memory 203 receives the print data stored in the reception memory 202 and records image data formed by performing an editing process on the print data.

The operation section 204 includes a display section (e.g., LED) for displaying the status of the image forming device 1 and an operation section (e.g. switch) used by the operator for inputting a command. The sensor group 205 includes various types of sensors for monitoring the operating status of the image forming device 1, such as a sheet position sensor, a temperature humidity sensor, a density sensor.

The power supply control section 206 controls a charging voltage power supply 207 for applying charging voltage to the charging rollers 63, a development voltage power supply 208 for applying development voltage to the development rollers 65, a supply voltage power supply 209 for applying supply voltage to the supply rollers 66, and a transfer voltage power supply 210 for applying transfer voltage to the transfer rollers 72. The head control section 211 sends image data recorded in the image data editing memory 203 to the print head 64 and controls the light emission of the print head 64.

The drive control section 212 controls a drive motor 213 for rotating the photosensitive drum 62 of each process unit 61. Incidentally, the charging roller 63 rotates following the rotation of the photosensitive drum 62, and the development roller 65 and the supply roller 66 rotate by transmission of the rotation from the photosensitive drum 62. The belt drive control section 214 controls a belt motor 215 for rotating the drive roller 73 for driving the transfer belt 71.

The fixation control section 216 includes a temperature regulation circuit and supplies electric current to a heater 217 of the fixation roller 81 based on an output signal from a thermistor 218 of the fixation device 80. The fixation drive control section 219 controls a fixation motor 220 for rotating the fixation roller 81 of the fixation device 80. Incidentally, the conveyance roller pair 83 and the ejection roller pair 84 rotate by transmission of rotation from the fixation motor 220.

The sheet supply conveyance control section 221 controls a sheet feed motor 222 and an electromagnetic clutch 223 for rotating the feed roller 53 of the send-out section 51, the sheet feed motor 224 and the electromagnetic clutch 225 for rotating the feed roller 35 of the manual feed tray 30, and the conveyance motor 226 for rotating the conveyance roller pairs 56 and 57 of the medium conveyance section 55.

Operation of Image Forming Device

Next, the operation of the image forming device 1 will be described with reference to FIG. 1, FIG. 11 and FIG. 12. The control section 200 of the image forming device 1 starts an image forming (print) operation when a print command and print data are received from a host device via the I/F control section 201. The control section 200 temporarily records the print data in the reception memory 202, generates image data by performing the editing process on the recorded print data, and records the image data in the image data editing memory 203.

Here, a case where the sheet P is fed from the manual feed tray 30 according to the print command will be described. To set the sheet P on the manual feed tray 30, the user rotates the lever 33 in a closing direction indicated by the arrow B2 in the state in which the manual feed tray 30 is at the open position as shown in FIG. 11. When the lever 33 rotates in the closing direction, the arm 33 a (FIG. 4) of the lever 33 depresses the sheet setting plate 32 against the biasing force of the spring 45.

The arm 33 a of the lever 33 is fitted in the groove 32 a of the sheet setting plate 32, and thereby the sheet setting plate 32 is maintained in the depressed state. In this state, a prescribed number of sheets P can be set between the sheet setting plate 32 and the pickup roller 34.

Further, when the user rotates the lever 33 in an opening direction indicated by the arrow B1, the depressing of the sheet setting plate 32 by the arm 33 a of the lever 33 is released. In this state, an upper surface of the sheet P set on the sheet setting plate 32 is pressed against the pickup roller 34 by the biasing force of the spring 45. Namely, the conveyance of the sheet P becomes possible.

In this state, the control section 200 makes the sheet supply conveyance control section 221 drive the sheet feed motor 224 and the electromagnetic clutch 225 to rotate the feed roller 35 clockwise in the drawing. The rotation of the feed roller 35 is transmitted to the pickup roller 34 via the idle roller 38. Accordingly, the pickup roller 34 rotates clockwise in the drawing.

By the rotation of the pickup roller 34, the sheet P pressed against the pickup roller 34 is sent out and sent into a nip part between the feed roller 35 and the retard roller 36. The feed roller 35 sends out the sheet P towards the medium conveyance section 55 while the retard roller 36 separates the sheet P from other sheets P one by one.

The sheet P that passed through the feed roller 35 and the retard roller 36 reaches the medium conveyance section 55. The sheet supply conveyance control section 221 drives the conveyance motor 226 to rotate the conveyance roller pairs 56 and 57. The conveyance roller pairs 56 and 57 convey the sheet P towards the image forming section 60.

The control section 200 makes the belt drive control section 214 drive the belt motor 215 to rotate the drive roller 73, and thereby make the transfer belt 71 travel. The transfer belt 71 adsorbs and holds the sheet P and conveys the sheet P. The sheet P passes through the process units 61K, 61Y, 61M and 61C in this order.

The control section 200 makes each process unit 61 form the toner image of its respective color. Specifically, the control section 200 makes the power supply control section 206 apply the charging voltage, the development voltage and the supply voltage respectively to the charging roller 63, the development roller 65 and the supply roller 66 of each process unit 61.

The control section 200 also makes the drive control section 212 rotate the drive motor 213 to rotate the photosensitive drum 62. The charging roller 63, the development roller 65 and the supply roller 66 also rotate accompanying the rotation of the photosensitive drum 62. With its charging voltage, the charging roller 63 uniformly charges the surface of the photosensitive drum 62.

The control section 200 also makes the head control section 211 perform light emission control on the print head 64 according to the image data recorded in the image data editing memory 203. The print head 64 exposes the surface of the photosensitive drum 62 to light and thereby forms an electrostatic latent image.

The electrostatic latent image formed on the surface of the photosensitive drum 62 is developed with the toner adhering to the development roller 65, and thereby the toner image is formed on the surface of the photosensitive drum 62. When the toner image approaches the surface of the transfer belt 71 by the rotation of the photosensitive drum 62, the power supply control section 206 applies the transfer voltage to the transfer roller 72. Thereby, the toner image formed on the photosensitive drum 62 is transferred to the sheet P on the transfer belt 71.

As above, the toner images of the respective colors formed in the process units 61K, 61Y, 61M, 61C are successively transferred to the sheet P and overlapped. The sheet P to which the toner images of the colors have been transferred is conveyed further by the transfer belt 71 and reaches the fixation device 80.

In the fixation device 80, the heater 217 has been heated by the fixation control section 216 and the fixation roller 81 has reached a prescribed fixation temperature. The sheet P conveyed to the fixation device 80 is heated and pressed between the fixation roller 81 and the pressure roller 82, and thereby the toner images are fixed on the sheet P.

The sheet P after the toner image fixation is ejected to the outside of the image forming device 1 by the conveyance roller pair 83 and the ejection roller pair 84 and is loaded on the stacker part 86. By this operation, the color image formation on the sheet P is completed.

Sheet Conveyance Operation on Manual Feed Tray

Next, a sheet conveyance operation on the manual feed tray 30 in the first embodiment will be described below with reference to a schematic diagram of FIG. 13. The medium conveyance device in the first embodiment can convey either a sheet P having high stiffness (Clark stiffness) (e.g., thick paper) as shown in FIG. 13A or a sheet P having low stiffness (e.g., standard paper or thin paper) as shown in FIG. 13B.

To inhibit the entry of a plurality of sheets P into the nip part between the feed roller 35 and the retard roller 36, a contact surface C to come in contact with the front end of the sheet P sent out from the pickup roller 34 has to be provided on the upstream side of the feed roller 35 and the retard roller 36. As the curvature radius of the contact surface C increases, the sheet P can climb over the contact surface C with greater ease.

As shown in FIG. 13A, in a case where the curvature radius of the contact surface C is small, there is a possibility that a sheet P having high stiffness cannot climb over the contact surface C and causes a conveyance error. In contrast, in a case where the curvature radius of the contact surface C is large as shown in FIG. 13B, sheets P having low stiffness are likely to climb over the contact surface C in a bundle and the multifeed can occur.

Therefore, in this first embodiment, the contact surface 21 a of the regulatory rib 21 having a large curvature radius R1 is projected into the conveyance path in a case where a sheet P having high stiffness is used, while the contact surface 22 a of the separatory dam 22 having a small curvature radius R2 is projected into the conveyance path in a case where a sheet P having low stiffness is used.

FIG. 14A is a diagram showing the medium conveyance device in a case where a sheet P having low stiffness (e.g., standard paper or thin paper) is fed. FIG. 14B is a diagram magnifying a part surrounded by the chain line circle in FIG. 14A. This description will be given while referring to the uppermost sheet in the stack of sheets on the sheet setting plate 32 as a sheet P1 and referring to the second and subsequent sheets P from the top of the stack as sheets P2.

As shown in FIG. 14A, when a sheet P having low stiffness is fed, the user rotates the switching lever 25 (FIG. 11) to an upper position. When the switching lever 25 is at the upper position, the separatory dam 22 is situated at the upper end position in the movable range as explained earlier with reference to FIG. 11.

Thus, the contact surface 22 a of the separatory dam 22 is situated above the contact surface 21 a of the regulatory rib 21 as shown in FIG. 14B. Namely, the contact surface 22 a of the separatory dam 22 projects into the conveyance path of the sheet P heading from the pickup roller 34 towards the feed roller 35. In other words, the contact surface 22 a of the separatory dam 22 is situated at a position for guiding the sheet P heading from the pickup roller 34 towards the feed roller 35.

In this state, the pickup roller 34 rotates and sends out the sheet P in the conveyance direction indicated by the arrow A. When a plurality of sheets P are sent out in the conveyance direction by friction between sheets P, the front end of the sheets P comes in contact with the contact surface 22 a of the separatory dam 22. Most of the sheets P are blocked by the contact surface 22 a of the separatory dam 22, while the uppermost sheet P1 coming in contact with the pickup roller 34 is conveyed in the conveyance direction indicated by the arrow A. There are also cases where some sheets P2 subsequent to the uppermost sheet P1 are conveyed in the same direction.

The sheet P sent out by the pickup roller 34 is sent to the nip part between the feed roller 35 and the retard roller 36. A predetermined rotational load occurs to the retard roller 36 by the torque limiter 37 (FIG. 6). Accordingly, even when a plurality of sheets P are about to enter the part between the feed roller 35 and the retard roller 36, only one sheet P1 coming in contact with the feed roller 35 is conveyed and the second and subsequent sheets P2 are prevented by the retard roller 36 from entering the nip part.

As above, the sheet P is separated as a single sheet and conveyed in the conveyance direction indicated by the arrow A. The sheet P1 conveyed by the feed roller 35 is conveyed via the conveyance roller pair 57 to the image forming section 60.

FIG. 15A is a diagram showing the medium conveyance device in a case where a sheet P having high stiffness (e.g., thick paper) is fed. FIG. 15B is a diagram magnifying a part surrounded by the chain line circle in FIG. 15A.

In the case of a sheet P having high stiffness, the user rotates the switching lever 25 (FIG. 11) to a lower position. When the switching lever 25 is at the lower position, the separatory dam 22 is situated at the lower end position in the movable range as explained earlier with reference to FIG. 11.

Thus, the contact surface 22 a of the separatory dam 22 withdraws downward compared to the contact surface 21 a of the regulatory rib 21 as shown in FIG. 15B. Accordingly, the contact surface 21 a of the regulatory rib 21 having the large curvature radius R1 projects into the conveyance path. In other words, the contact surface 21 a of the regulatory rib 21 is situated at a position for guiding the sheet P heading from the pickup roller 34 towards the feed roller 35.

In this state, the pickup roller 34 rotates and sends out the sheet P in the conveyance direction indicated by the arrow A. When a plurality of sheets P are sent out in the conveyance direction by friction between sheets P as mentioned earlier, the front end of the sheets P comes in contact with the contact surface 21 a of the regulatory rib 21. Most of the sheets P are blocked by the contact surface 21 a of the regulatory rib 21, while the uppermost sheet P1 coming in contact with the pickup roller 34 is conveyed in the conveyance direction indicated by the arrow A. There are also cases where some sheets P2 subsequent to the uppermost sheet P1 are conveyed in the same direction.

The sheet P sent out by the pickup roller 34 is sent to the nip part between the feed roller 35 and the retard roller 36. Similarly to the case of sheets P having low stiffness, also in the case of sheets P having high stiffness, only one sheet P1 coming in contact with the feed roller 35 is conveyed and the second and subsequent sheets P2 are prevented by the retard roller 36 from entering the nip part. As above, the sheet P is separated as a single sheet, conveyed in the conveyance direction indicated by the arrow A, and conveyed via the conveyance roller pair 57 to the image forming section 60.

As above, in a case where a sheet P having high stiffness is used, the contact surface 21 a of the regulatory rib 21 having the large curvature radius R1 is projected into the conveyance path, and thereby the sheet P is facilitated to climb over the contact surface 21 a and the conveyance error is inhibited. In contrast, in a case where a sheet P having low stiffness is used, the contact surface 22 a of the separatory dam 22 having the small curvature radius R2 is projected into the conveyance path, and thereby a plurality of sheets climbing over the contact surface 22 a in a bundle, namely, the multifeed, is inhibited.

By using one of the contact surfaces 21 a and 22 a differing in the curvature radius according to the stiffness of the sheet P, the multifeed and the conveyance error can be effectively inhibited for both of sheets P having high stiffness and sheets P having low stiffness.

Further, the height of the contact surface 21 a of the regulatory rib 21 when the contact surface 21 a is situated in the conveyance path is slightly lower than the height of the contact surface 22 a of the separatory dam 22 when the contact surface 22 a is situated in the conveyance path. With this configuration, the sheet P having high stiffness is facilitated to climb over the contact surface 21 a.

The curvature radii R1 and R2 of the contact surface 21 a of the regulatory rib 21 and the contact surface 22 a of the separatory dam 22 are determined according to the types of sheets P to be conveyed. For example, in a case where the grammage of the sheet P used for the image forming device 1 is in a range of 64 to 250 gsm, the curvature radius R1 is desired to be 2.0 mm or more and the curvature radius R2 is desired to be 0.3 mm or less. In this case, the regulatory ribs 21 are used for sheets P whose grammage is 68 to 250 gsm, and the separatory dams 22 are used for sheets P whose grammage is 64 to 68 gsm.

Incidentally, while the switching between the regulatory ribs 21 and the separatory dams 22 is made by using the manual switching lever 25 in the above description, the way of switching is not limited to such a configuration and it is also possible to switch between the regulatory ribs 21 and the separatory dams 22 by using an actuator such as a motor, for example.

Further, while the regulatory rib 21 has the contact surface 21 a having a large curvature radius R1 and the separatory dam 22 has the contact surface 22 a having a small curvature radius R1 in the above description, it is permissible even if the regulatory rib 21 has a contact surface having a small curvature radius and the separatory dam 22 has a contact surface having a large curvature radius.

Effect of Embodiment

As described above, in the first embodiment, the regulatory rib 21 and the separatory dam 22 (medium contact part) have a plurality of contact surfaces 21 a and 22 a which are switchable according to the type of the sheet P (medium) and differ in the curvature radius. Therefore, the conveyance error and the multifeed can be inhibited for both of sheets P having high stiffness such as thick paper and sheets P having low stiffness such as thin paper. Accordingly, limitation on usable sheets can be relaxed.

Further, the separatory dam 22 is movable with respect to the regulatory rib 21 and the switching between a first state in which the contact surface 21 a of the regulatory rib 21 projects into the conveyance path and a second state in which the contact surface 22 a of the separatory dam 22 projects into the conveyance path is made by the movement of the separatory dam 22. Thus, the switching between the contact surfaces 21 a and 22 a according to the type of the sheet can be made with a simple configuration.

Furthermore, since the switching between the first state and the second state is made with the switching lever 25 as a movement operation part, the user can make the selection of the appropriate contact surface 21 a or 22 a according to the type of the sheet to be used.

Moreover, since the height of the contact surface 21 a of the regulatory rib 21 when the contact surface 21 a comes in contact with the sheet P is lower than the height of the contact surface 22 a of the separatory dam 22 when the contact surface 22 a comes in contact with the sheet P, a sheet P having high stiffness is facilitated to climb over the contact surface 22 a, for example, and the conveyance error can be effectively prevented.

In addition, since the regulatory ribs 21 and the separatory dams 22 are arranged on both sides of the feed roller 35 in the Y direction, it is possible to come in contact with the sheet P at two positions in the width direction and thereby enhance the effect of separating the sheets P.

While this description has been given of a configuration in which the contact surfaces 21 a and 22 a of the regulatory rib 21 and the separatory dam 22 differ from each other in the curvature radius, it is permissible if the contact surfaces 21 a and 22 a differ from each other in the shape, not necessarily in the curvature radius. For example, it is also possible to form the contact surfaces 21 a and 22 a of the regulatory rib 21 and the separatory dam 22 as tapered surfaces whose taper angles differ from each other.

Second Embodiment

Next, a second embodiment of the present invention will be described below. FIG. 16 is a sectional side view showing a medium conveyance device in the second embodiment. Incidentally, components in the second embodiment identical with those in the first embodiment are assigned the same reference characters as in the first embodiment.

In the second embodiment, the configuration of the separatory dam (referred to as a rotative dam 26) differs from that in the first embodiment while the configuration of the regulatory rib 21 is the same as that in the first embodiment. The rotative dam 26 in the second embodiment has a shaft hole 26 b to be fitted on a rotary shaft 16 (FIG. 17B) provided on the device frame 10, and is attached to the device frame 10 to be rotatable.

The rotative dam 26 has an arc-shaped guide groove 26 c (hole part) centering at the shaft hole 26 b. Into the guide groove 26 c, a guide pin 17 (regulation part) provided on the device frame 10 is fitted. A rotation range of the rotative dam 26 is regulated by the engagement of the guide groove 26 c and the guide pin 17.

The rotative dam 26 has a contact surface 26 a that projects into the conveyance path between the pickup roller 34 and the feed roller 35. The curvature radius R3 of the contact surface 26 a of the rotative dam 26 is smaller than the curvature radius R1 of the contact surface 21 a of the regulatory rib 21.

Further, between the rotative dam 26 and a spring seat 47 formed on the device frame 10, a spring 48 as a coil spring is arranged in a compressed state. By this spring 48, the rotative dam 26 is pressed in the direction in which the contact surface 26 a projects into the conveyance path.

In normal times, the contact surface 26 a of the rotative dam 26 is situated above the contact surface 21 a of the regulatory rib 21 and projects into the conveyance path by the biasing force of the spring 48. In contrast, when the rotative dam 26 is rotated in the direction indicated by the arrow D against the biasing force of the spring 48, the contact surface 26 a of the rotative dam 26 withdraws downward from the conveyance path. In this state, the contact surface 21 a of the regulatory rib 21 projects into the conveyance path.

In this example, the biasing force of the spring 48 is set so that the rotative dam 26 is not rotated just by the contact of the front end of a sheet P having low stiffness (e.g., standard paper) with the contact surface 26 a of the rotative dam 26 and the rotative dam 26 is rotated in the direction of the arrow D when the front end of a sheet P having high stiffness (e.g., thick paper) comes in contact with the contact surface 26 a of the rotative dam 26. The rotative dam 26 swings according to the stiffness of the sheet P so that the switching between the contact surfaces 21 a and 26 a is made.

Therefore, the switching lever 25 (FIG. 11) described in the first embodiment is not provided in the second embodiment. The rest of the configuration in the second embodiment is the same as that described in the first embodiment.

Next, the sheet conveyance operation in the second embodiment will be described below. FIG. 17A is a diagram showing the medium conveyance device in a case where a sheet P having low stiffness (e.g., standard paper) is fed. FIG. 17B is a diagram magnifying a part surrounded by the chain line circle in FIG. 17A. FIG. 17C is an enlarged view showing a case where a sheet P having high stiffness is fed.

As shown in FIG. 17B, when the pickup roller 34 rotates, the sheet P is sent out in the conveyance direction indicated by the arrow A and the front end of the sheet P comes in contact with the contact surface 26 a of the rotative dam 26. In the case of a sheet P having low stiffness, the rotative dam 26 does not rotate since the biasing force of the spring 48 is stronger than the force the contact surface 26 a of the rotative dam 26 receives from the front end of the sheet P.

Accordingly, the contact surface 26 a of the rotative dam 26 is maintained in the state of projecting into the conveyance path. The contact surface 26 a of the rotative dam 26 blocks most of the sheets P, while the uppermost sheet P1 coming in contact with the pickup roller 34 is conveyed in the conveyance direction indicated by the arrow A. There are also cases where some sheets P2 subsequent to the uppermost sheet P1 are conveyed in the same direction.

The sheet P sent out in the conveyance direction indicated by the arrow A is separated as a single sheet by the feed roller 35 and the retard roller 36 and is conveyed to the conveyance roller pair 57 in the image forming device 1 as described in the first embodiment.

In contrast, in the case of a sheet P having high stiffness, the force the contact surface 26 a of the rotative dam 26 receives from the front end of the sheet P is stronger than the biasing force of the spring 48, and thus the rotative dam 26 rotates in the direction indicated by the arrow D as shown in FIG. 17C.

Accordingly, the contact surface 26 a of the rotative dam 26 withdraws from the conveyance path and the contact surface 21 a of the regulatory rib 21 projects into the conveyance path. The contact surface 21 a of the regulatory rib 21 blocks most of the sheets P, while the uppermost sheet P1 coming in contact with the pickup roller 34 is conveyed in the conveyance direction indicated by the arrow A. There are also cases where some sheets P2 subsequent to the uppermost sheet P1 are conveyed in the same direction.

The sheet P sent out in the conveyance direction indicated by the arrow A is separated as a single sheet by the feed roller 35 and the retard roller 36 and is conveyed to the conveyance roller pair 57 in the image forming device 1 similarly to the case of the sheet P having low stiffness.

As above, in a case where a sheet P having high stiffness is used, the contact surface 21 a of the regulatory rib 21 having the large curvature radius R1 projects into the conveyance path, and thus the sheet P is allowed to climb over the contact surface 21 a and the conveyance error is inhibited. In a case where a sheet P having low stiffness is used, the contact surface 26 a of the rotative dam 26 having the small curvature radius R1 projects into the conveyance path, and thus a plurality of sheets P climbing over the contact surface 21 a in a bundle, namely, the multifeed, is inhibited.

Incidentally, as described in the first embodiment, in a case where the grammage of the sheet P is in the range of 64 to 250 gsm, the curvature radius R1 of the contact surface 21 a of the regulatory rib 21 is desired to be 2.0 mm or more and the curvature radius R3 of the contact surface 26 a of the rotative dam 26 is desired to be 0.3 mm or less.

As described above, in the second embodiment, the switching between the contact surfaces 21 a and 26 a is made by the swinging of the rotative dam 26 according to the stiffness of the sheet P, and thus the switching lever 25 becomes unnecessary and the actuator for driving the switching lever 25 also becomes unnecessary in addition to achieving the effects described in the first embodiment. Accordingly, the production cost can be reduced. Further, since the user does not need to operate the switching lever, prevention of erroneous selection can also be achieved.

Incidentally, while the regulatory rib 21 has the contact surface 21 a having a small curvature radius and the rotative dam 26 has the contact surface 26 a having a large curvature radius in the above description, it is permissible even if the regulatory rib 21 has a contact surface having a large curvature radius and the rotative dam 26 has a contact surface having a small curvature radius.

Further, while this description has been given of a configuration in which the contact surfaces 21 a and 26 a of the regulatory rib 21 and the rotative dam 26 differ from each other in the curvature radius, it is permissible if the contact surfaces 21 a and 26 a differ from each other in the shape, not necessarily in the curvature radius. For example, it is also possible to form the contact surfaces 21 a and 26 a of the regulatory rib 21 and the rotative dam 26 as tapered surfaces whose taper angles differ from each other.

While the description of the above embodiments has been given of image forming devices for forming color images, the present invention is applicable also to image forming devices for forming unicolor (monochrome) images. Further, the present invention is employable for image forming devices for forming an image on a medium by means of electrophotography (e.g., copying machines, facsimile machines, printers, multi-function peripherals, etc.) and their fixation devices, for example. 

What is claimed is:
 1. A medium conveyance device comprising: a medium setting part on which a medium is set; a first roller coming in contact with the medium set on the medium setting part, the first roller sending out the medium in a conveyance direction; a second roller situated on a downstream side of the first roller in the conveyance direction, the second roller conveying the medium sent out by the first roller; and a medium contact part arranged in a conveyance path between the first roller and the second roller, the medium contact part coming in contact with the medium, wherein the medium contact part has a plurality of contact surfaces switchable according to a type of the medium, the plurality of contact surfaces differing in shape.
 2. The medium conveyance device according to claim 1, wherein the medium contact part has a first contact surface and a second contact surface, a curvature radius of the second contact surface differs from a curvature radius of the first contact surface, and switching between the first contact surface and the second contact surface is made according to the type of the medium.
 3. The medium conveyance device according to claim 2, wherein the curvature radius of the first contact surface is not less than 2.0 mm, and the curvature radius of the second contact surface is not more than 0.3 mm.
 4. The medium conveyance device according to claim 2, wherein the medium contact part includes a movable part having one of the first contact surface and the second contact surface and a fixed part having the other of the first contact surface and the second contact surface, and switching between a first state in which the first contact surface is situated in the conveyance path and a second state in which the second contact surface is situated in the conveyance path is made by moving the movable part with respect to the fixed part.
 5. The medium conveyance device according to claim 4, further comprising a movement operation part that is operated by a user and moves the movable part.
 6. The medium conveyance device according to claim 4, further comprising a biasing member, wherein the movable part is movable in a direction of projecting into the conveyance path and in a direction of withdrawing from the conveyance path and is pressed towards the conveyance path by the biasing member, and the other of the first contact surface and the second contact surface projects into the conveyance path when the movable part withdraws from the conveyance path due to contact with the medium.
 7. The medium conveyance device according to claim 6, wherein the movable part is rotatable with respect to the fixed part.
 8. The medium conveyance device according to claim 7, wherein the fixed part has a regulation part regulating rotation of the movable part, the movable part has a hole part engaging with the regulation part, and the rotation of the movable part is regulated by engagement of the regulation part and the hole part.
 9. The medium conveyance device according to claim 2, wherein a height of the first contact surface when the first contact surface comes in contact with the medium and a height of the second contact surface when the second contact surface comes in contact with the medium differ from each other.
 10. The medium conveyance device according to claim 1, wherein the first roller and the second roller are arranged at a central part of the medium in a width direction of the medium, and the medium contact part is arranged on both sides of the first roller and the second roller in the width direction of the medium.
 11. The medium conveyance device according to claim 1, further comprising a separation roller arranged so as to face the second roller.
 12. The medium conveyance device according to claim 10, further comprising a torque limiter, wherein the separation roller comes in contact with the second roller and is rotatably supported via the torque limiter.
 13. An image forming device comprising: the medium conveyance device according to claim 1; and an image forming section that forms an image on the medium conveyed by the medium conveyance device. 